The present invention relates to a cylinder head, gasket used in an engine.
A cylinder head gasket is known in the art which comprises a first and a second gasket plate disposed in overlapping relationship, held sandwiched between a cylinder head and a cylinder block and-each having a combustion chamber opening formed therein in alignment with a cylinder bore.
In a cylinder head gasket of the type described, as an explosion pressure of an engine increases, a gas in a combustion chamber may blow through a clearance between the cylinder head gasket and the cylinder head, between the cylinder head gasket and the cylinder block or between a first and a second gasket substrate which form together the cylinder head gasket.
For purposes of reducing the weight of an engine, a cylinder block which is made from aluminum has recently been employed, with a cast iron liner being usually provided on the cylinder bore in order to secure an abrasion resistance thereof. Such a liner may be secured in place by a press fit or by a casting technique. In the press fit technique, the end of the liner is formed with a flange, which is disposed in abutment against an offset step formed on the block, so that the both parts may be positioned and theandliner can be secured by a press fit in the cylinder block.
For a multi-cylinder engine including a plurality of press fit liners, if each liner is mounted on the cylinder block in an even manner, there often results a delicate difference in the amount of projection above the surface of the cylinder block from liner to liner.
Accordingly, when the cylinder head gasket is interposed between the cylinder head and the cylinder block, which are then clamped together by clamping bolts, a failure of a bead on the cylinder head gasket may occur in a region thereof which is contacted by a liner which projects above the surface of the cylinder block to cause an excessively high pressure of contact or the offset step on the cylinder block, which is abutted by the liner flange, may be deformed to cause a blow-through of a gas in the combustion chamber. The likelihood of causing a blow-through of a gas in the combustion chamber also exists in a region of the cylinder head gasket which is contacted by a liner which remains depressed below the surface of the cylinder block to present an excessively low pressure of contact.
When the cylinder head and the cylinder block are clamped together by the clamping bolts, the surface pressure is high in a region located adjacent to one of the bolts while the surface pressure decreases with a distance from the bolts, causing a degradation in the sealing performance of some engines at a distance from the clamping bolts, again giving rise to the likelihood of producing a blow-through of a gas in the combustion chamber.
The present invention provides a cylinder head gasket capable of preventing the occurrence of a blow-through of a combustion gas more effectively.
The invention also provides a cylinder head gasket which allows the occurrence of a blow-through of a combustion gas to be prevented by enabling a surface pressure which is as even as possible to be achieved when a cylinder head and a cylinder block are clamped together by clamping bolts.
Specifically, according to a first aspect of the invention, there is provided a cylinder head gasket including a first and a second gasket substrate disposed in overlapping relationship, held sandwiched between a cylinder head and a cylinder block and each having a combustion chamber opening formed therein in alignment with a cylinder bore, the first gasket substrate being disposed toward the cylinder head and formed with a first inner projection surrounding the combustion chamber opening and projecting toward the cylinder head and the second gasket substrate being disposed toward the cylinder block and formed with a second inner projection surrounding the combustion chamber opening and projecting toward the cylinder block, the first and the second gasket substrate being disposed in overlapping relationship to define a clearance between the first and the second inner projection which project in opposite direction from each other, the first and the second gasket substrate being held sandwiched between the cylinder head and the cylinder block in a manner to cause a plastic deformation of the first and the second inner projection toward the clearance defined therebetween.
According to a second aspect of the invention, a cylinder head gasket of a conventional type as mentioned above is characterized in that the first gasket substrate which is disposed toward the cylinder head is formed with a first inner projection surrounding the combustion chamber opening and projecting toward the cylinder head and including a radially central part which projects toward the cylinder block, that the second gasket substrate which is disposed toward the cylinder block is formed with a second inner projection surrounding the combustion chamber opening and projecting toward the cylinder block and including a radially central part which projects toward the cylinder head, and that the first and the second gasket substrate are disposed in overlapping relationship such that at least when they are assembled into an engine, the radially central part the first inner projection and the radially central part of the second inner projection are disposed to be in close contact with each other continuously in the circumferential direction.
Accordingly, according to the first aspect of the invention, when the cylinder head gasket is held sandwiched between the cylinder head and the cylinder block, which are clamped together by clamping bolts, the first inner projection of the first gasket substrate and the second inner projection of the second gasket substrate undergo a plastic deformation in a direction toward the clearance defined therebetween.
If there is a delicate difference in the amount of projection above the surface pressure of the cylinder block from liner to liner, or if the surface pressure is high in a region adjacent to clamping bolts while it is low away therefrom, both inner projections will undergo a magnitude of a plastic deformation which varies in accordance with the surface pressure, with a consequence that there is secured an even pressure of contact, enabling a local blow-through to be prevented.
According to the second aspect of the invention, the radially central part of the first inner projection which projects toward the cylinder block and the radially, central part of the second inner projection which projects toward the cylinder head are disposed to be in close contact with each other, continuously in the circumferential direction, and accordingly, the pressure of any combustion gas which tends to blow through a clearance therebetween urges the first inner projection toward the cylinder head and urges the second inner projection toward the cylinder block. As the first inner projection is urged against the cylinder head by the gas pressure, the sealing performance thereof is improved. Similarly, as the second inner projection is urged against the cylinder block by the gas pressure, the sealing performance thereof is improved. In addition, when the first inner projection is urged against the cylinder head and the second inner projection is urged against the cylinder block, reactions from these urging effects drive the radially central parts of the first and the second inner projection into more tight contact with each other, thus improving the sealing performance in such area.